In contact lens technology contact lenses are provided with a manufactured curvature and it is critical to the proper manufacturing and functioning of a contact lens that it be curved accurately. One reason for the need for accurate curvature is that the lens must locate on the eye such that there is no compression of the eye or eye blood vessels nor general eye discomfort caused to the wearer if the lens is inaccurately curved. The curvature is also critical to the particular astigmatic requirements of the eye.
The above problems can occur where the curve of the lens is not compatible with the radius of curvature of the particular eye surface of the wearer of the lens.
In addition, if the curvature of the lens is not accurately formed, decentering and wedging effects can be caused when it is on the eye. This can lead to eye damage and can affect the performance of the lens.
The critical zone of a contact lens is the optic zone located between the lens flange which is peripheral to the optic zone. The optic zone and flange meet at an interphase point known as a lenticulation on the outer surface of the lens. These various parts of the lens can be lathed out to different thicknesses from a blank which is formed from a polymer button. It is important that the optical zone be toroidal, and this is achieved by the curvature of the lens. The toric lens has an infinite number of powers to correspond to the particular power of the cornea of the eye.
The toricity of the lens must be constant for a particular lens.
The art of toric lens manufacture lies in the production of a lens which will be sufficiently accurate for the practitioner and which will sit with a tight degree of accuracy on the eye and which will be appropriate for the particular needs of the user. For these requirements to be achieved accurate curvature of the lens is essential.
Whilst there are a number of methods existing which are used for buckling lenses there are disadvantages which have been manifested with these prior art methods.
One of the commonly used methods of manufacture of toric contact lenses is to buckle the spherical surface of a lens blank by two pins located near the edge of the lens.
The buckled lenses are produced by crimping of the lens and by exerting lateral pressure exerted across the diameter of the lens. The stress is relieved from the lens when the crimping is released. When the lens is allowed to release the buckle is so created, a curve is thereby formed in the lens proportional to the degree of buckle or crimp applied.
The main problem with this method is that the buckle or crimp on the surface continually must be measured with a Radiuscope and the amount of buckle or crimp adjusted until the correct sagittal difference between the two meridians of the lens has been achieved.
This trial and error process is slow and tedious by comparison to the method and apparatus used in the present invention.
The present invention seeks to overcome the inefficiency of the prior art processes for buckling contact lenses by providing a means to produce an accurately curved toric surface lens according to prescription in a much shorter time.
By using the device and method of the present invention any number of lenses can be buckled to a preset degree with the same accuracy and without any further adjustment to the machine.
The invention also enables the speedy production of an unlimited number of buckled toric lenses of the same curvature by presetting the device to the required curvature.
Considerable production time and hence cost is saved because it is no longer necessary to make trial and error adjustments to the buckle for each individual lens until the desired lens curvature is produced.
In employing the prior art methodology uncrimping has always been a critical stage in lens manufacture, as the stress relieving can alter the curvature of the lens. This necessitates the use of the aforementioned monitoring Radioscope to continually read the crimping radii until the correct curvature has been achieved.
Using the machine of the present invention it will no longer be necessary to constantly monitor the lens radii, as this is accurately set by the machine itself in accordance with the degree of buckling.
It has previously been difficult to ensure that the lens to be crimped is crimped exactly along the meridian of the lens.
The present invention by virtue of the facility for pre-setting of the machine and the method of buckling used eliminates this problem.
With the present invention, it is now possible to mass produce astigmatic contact lenses using a buckling machine without the need for constant adjustment of the machine each time a lens is buckled except when a variation in the astigmatic lens is required.